1. Field of the Invention
The present invention relates to novel synergistic insecticidal compositions which are mixtures of water-soluble xanthene dyes, and which comprise at least one insecticidally active dye chosen from amongst erythrosine and Rose Bengal in admixture with the essentially non-insecticidally active fluorescein sodium, and to a method of combating insects with said mixtures.
2. Description of the Prior Art
Both erythrosine and Rose Bengal employed individually, as well as in admixture with each other, are known to be effective as insecticides. In the most relevant prior art, the insecticidal activity is generally attributed to a photodynamic action of visible light on insects or their larvae pretreated with the dyes in the dark followed by exposure to visible light.
A. Barbieri, Rivista di Malariologica 7:456-63 (1928) discloses that when 15 mosquito (Culex) larvae were treated with an aqueous solution of Rose Bengal at a concentration of 1:30,000 and held in the dark for several hours, all the larvae died within three hours on being exposed to diffuse solar light. Barbieri also reported that "several larvae and pupae", when treated with an aqueous solution containing a mixture of erythrosine and Rose Bengal at a concentration of 1:30,000 and held in the dark for several hours, died (except for 1 pupae) within two and a half hours on being exposed to diffuse (solar) light.
H. Schildmacher, Biol. Zentr. 69:468-77 (1950) discloses that Rose Bengal and erythrosine, each used independently at a concentration of 1:100,000, have larvicidal activity against second and third instar larvae of the mosquito (Anopheles maculipennis) upon immediate exposure of the treated larvae to direct sunlight for 130 minutes, but that Uranin (fluorescein sodium) was rejected as a potential insecticide because, under the same test conditions, 32 out of 40 larvae survived as compared to 39 out of 40 surviving among the untreated control larvae. In the case of erythrosine, 5 out of 40 larvae survived, and in the case of Rose Bengal, none of the 40 larvae survived. This author also reports that survival prior to exposure to light of larvae pretreated in the dark with erythrosine and Rose Bengal was equal to or better than survival of larvae held only in water in the dark for the same period of time.
J. E. Fondren, Jr. and J. R. Heitz, Environmental Entomology 7, no. 6:843-6 (1978) disclose that erythrosine and Rose Bengal singly fed to adult face flies (Musca autumnalis), each at a concentration of 5.times.10.sup.3 M in a 2 percent milk sugar solution, and the flies held in the dark followed by exposure to fluorescent light, produces LT.sub.50 values of 8.16 hours and 1.53 hours, respectively while the same concentration of fluorescein sodium produces a LT.sub.50 value greater than 48 hours.
J. R. Broome, M. F. Callaham and J. R. Heitz, Environmental Entomology 4, no. 6:883-886 (1975) disclose that both erythrosine and Rose Bengal are photodynamically lethal to the black imported fire ant (Solenopis richteri) when separately fed to the test insect in the dark for 24 hours in a concentration of 5.times.10.sup.-3 M in a 1 percent sucrose solution followed by exposure to fluorescent light for varying periods of time.
T. P. Yoho, J. E. Weaver, and L. Butler, J. Economic Entomology 64:972-3 (1971) disclose that house flies (Musca domestica) prefed (in the dark) either erythrosine or Rose Bengal dissolved in milk sugar solution at a concentration of 0.125 percent have a mortality after exposure to natural light of 89 and 100 percent, respectively, while fluorescein sodium fed under the same conditions and concentrations exhibits no mortality.
J. R. Heitz and W. W. Wilson in Disposal and Decontamination of Pesticides, ACS Symposium Series, No. 73 (1978) disclose that the xanthene dyes erythrosine, Rose Bengal and fluorescein sodium have half-lives in visible light on the order of hours and that the photodegraded residual material is less toxic to insects (house flies) and bacteria than the undegraded dyes.